<div dir="ltr"><div class="gmail_quote"><div id="m_7488737673195001721mimemail-body" class="m_7488737673195001721elog-logentry-notify"><div id="m_7488737673195001721center"><div id="m_7488737673195001721main"><article id="m_7488737673195001721node-643319" class="m_7488737673195001721node m_7488737673195001721node-logentry m_7488737673195001721article m_7488737673195001721ia-n m_7488737673195001721clearfix"><header class="m_7488737673195001721node-header"><h1 class="m_7488737673195001721node-title"><a href="https://logbooks.jlab.org/entry/3570432" rel="bookmark" target="_blank">fast raster of GlueX photon beam is working!</a>
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<p class="m_7488737673195001721author-datetime">
Lognumber <a href="https://logbooks.jlab.org/entry/3570432" class="m_7488737673195001721lognumber" target="_blank">3570432</a>. Submitted by <a href="https://logbooks.jlab.org/user/jonesrt" target="_blank">jonesrt</a> on <time datetime="2018-05-01T17:40:49-0400">Tue, 05/01/2018 - 17:40</time>. </p>
<p class="m_7488737673195001721last-update">
Last updated on <time datetime="2018-05-01T17:57:29-0400">Tue, 05/01/2018 - 17:57</time></p>
<table class="m_7488737673195001721field-vitals"><tbody><tr><th>Logbooks: </th><td><a href="https://logbooks.jlab.org/book/hdlog" target="_blank">HDLOG</a> <a href="https://logbooks.jlab.org/book/elog" target="_blank">ELOG</a></td></tr></tbody></table></div>
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We are getting a good spread in the beam position now with the fast raster turned on. The plots of the raw wire signals make it clear when the fast raster is turned on. Note how the inner wedge currents go from a narrow line to a broad band, which is a signature of the beam oscillating in position. The second and third plots show a zoomed-in view of two of this raw wire signals, where the clear presence of a ~25Hz oscillation is seen. The split between the two plots in the top row comes because the active collimator DAQ decided to switch files in the middle of the raster period. The plots that follow below are taken from the 3-4 minute period after the start of the new AC daq run.
<table><tbody><tr><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:00745297cb44ce208447481024d67d48@logbooks.jlab.org" width="766" height="522" alt=""></div></td><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:5af269fd9062310c845ea73513cadcde@logbooks.jlab.org" width="766" height="522" alt=""></div></td></tr><tr><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:c6f373cc9f2a20f1126d852111e58cc9@logbooks.jlab.org" width="766" height="522" alt=""></div></td><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:08c01b185e1d09160ed37945e4500c60@logbooks.jlab.org" width="766" height="522" alt=""></div></td></tr></tbody></table>
The following plots show the Fourier transform of the signal during the brief period (3-4 minutes of beam) after the start of the new run. Notice that two distinct frequency peaks show up in the Fourier spectrum, consistent with 23 Hz and 27 Hz as programmed by the Operator. The frequency resolution in these plots is limited by the 0.5s width of the active collimator readout buffer. One thing I would like to try during a following run is to increase the sample period in the AC daq. We don't actually need anything like the 16Hz sampling frequency we have now with the sample-averaging factor of 32. We could change this to 512 and still cover the full bandwidth of the AC, thereby increasing our sample period to 8s, more than enough to clearly resolve the two driving frequencies. Still, just from these plots one can see not just the dominant two driving frequencies at 23 and 27 Hz, but their first 5 or maybe 6 harmonics as well. And this is just with 3-4 minutes of running.
<table><tbody><tr><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:86c639179ddf1925af180cec07f7a807@logbooks.jlab.org" width="766" height="522" alt=""></div></td><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:7c827a961a101e8f99b684454f026336@logbooks.jlab.org" width="766" height="522" alt=""></div></td></tr><tr><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:de7405261d2c75cbd1d63b5eff5534fd@logbooks.jlab.org" width="766" height="522" alt=""></div></td><td><div class="m_7488737673195001721image-wrapper"><img class="m_7488737673195001721image-style-plentybig" src="cid:9f404f62009740994d683a59cf10f869@logbooks.jlab.org" width="766" height="522" alt=""></div></td></tr></tbody></table>
Note the presence of both frequencies in the inner x and y raw signals. This is not surprising, as the oscillating correctors are far upstream in the beam line, and there is plenty of opportunity in steering elements between them and the radiator to introduce coupling between the x and y components of the motion. </div>
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